1. Field of the Invention
This invention relates to a multiple feed detection device for detecting a feed of two or more overlapped sheets (multiple feed) when sheets are carried along a carriage path, and more particularly to a method and a device for detecting a multiple feed suitable for the multiple feed detection of prints.
2. Description of the Related Art
A collator shown in FIGS. 8, 9A, and 9B is known as an apparatus for collating a plurality of different prints by overlapping them one by one from the first page to make bundles of a desired number of copies of the prints.
FIG. 8 shows an external view illustrating an entire collator, FIG. 9A shows a partially enlarged sectional view of each bin taken from FIG. 8, and FIG. 9B shows a view illustrating each bin as viewed in the direction indicated by the arrow A in FIG. 9A. In FIG. 8, arrows indicate the flow of sheets for each bin.
A collator 1 comprises a plurality of bins (10 bins in an example of FIG. 8) 2 in which different prints (sheets) are to be set. The bins 2 (21 to 210) are arranged in parallel in spaced apart relation provided vertically with respect to a body 3 and disposed to be protruded with a predetermined distance from the front surface of the body 3.
A sheet discharge tray 5 for collating and discharging prints 4 which are fed from each bin 2 one by one is disposed to be protruded with a predetermined distance from the front surface of the body 3 at the lowest part of the body 3. A carriage mechanism is provided inside the body 3, e.g., carrier rollers or carrier belts for carrying the prints 4 fed from each bin 2 onto the sheet discharge tray 5.
Each bin 2 comprises a sheet feed base 6 on which the prints 4 are set. The sheet feed base 6 includes a fixed part 6a and a movable part 6b which is vertically movable by a shift mechanism driven by a motor (not shown). A sheet-detecting sensor 7 for detecting any presence of the prints 4 to be set, e.g., a reflector-type sensor, is disposed in the movable part 6b. A sheet feed fence 8 movable in accordance with the size of the prints 4 to be set is disposed on the sheet feed base 6. The sheet feed fence 8 in FIG. 9B is provided to be fixed at the right side and movable in accordance with the size (width) of the prints at the left side.
A sheet feed roller 9 and a handling plate 10 for carrying the prints 4 set on the sheet feed base 6 one by one from the top to the body 3 are provided to be opposed to one another in each bin 2. Auxiliary rollers 11 for keeping the prints 4, e.g., from being curled, are disposed at both sides of the sheet feed roller 9. The rotation axis 12 of the sheet feed roller 9 and the auxiliary rollers 11 is connected through a sheet feed clutch 13 to a main motor (drive motor 26). The sheet feed roller 9 and the auxiliary rollers 11 rotate by means of drive of the main motor in a clockwise direction in FIG. 9A.
Multiple feed sensors 15 as a sheet detector for detecting a multiple feed of the prints 4 to be fed are disposed around a carriage path between the sheet feed roller 9 of each bin 2 and the carriage mechanism of the body 3.
The multiple feed sensors 15 are constituted by a transmission-type of optical sensors comprising a light emitting sensor 15a and a light receiving sensor 15b. The light emitting sensor 15a is, for example, constituted by a light emitting diode, a laser diode, or a lamp. The light emitting sensor 15a is disposed at a predetermined distance apart from the carriage path 16 along which the prints 4 are fed.
The light receiving sensor 15b is, for example, constituted by a photodiode. The light receiving sensor 15b is disposed to be opposed to the light emitting sensor 15a at a predetermined distance apart from the carriage path 16, e.g., in an equally spaced apart relation between the light emitting sensor 15a and the carriage path 16 such that the carriage path 16 on which the prints 4 are fed is sandwiched between the sensors.
At the position of the multiple feed sensor 15, if the prints 4 are not carried, the light emitted from the light emitting sensor 15a is directly received by the light receiving sensor 15b, whereas if the prints 4 are carried, the light transmitted through the prints 4 is received by the light receiving sensor 15b. 
In the collator 1 as constituted above, when the prints 4 having pages 1 to 10 are respectively set to the bins 21 to 210 in order, e.g., the prints 4 of page 1 to 21, the prints 4 of page 2 to 22, the prints 4 are fed one by one subsequently from the bin 21 positioned in the highest part, and discharged onto the sheet discharge tray 5. This allows the collated prints 4 to be discharged as a copy of the pages 1 to 10 onto the sheet discharge tray 5.
Each of the prints 4 set in each of the bins 2 is fed inside the body 3 through the following states: that is, the state where it is approaching carrier rollers 17 of the carriage mechanism of the body 3 as shown in FIG. 01A, the state where it has reached the carrier rollers 17 and a loose is then produced as shown in FIG. 10B, the state where it is pressed by the sheet feed roller 9 and the carrier rollers 17 so that the position of it passing between the multiple feed sensors 15 is fixed as shown in FIG. 10C, and the state where the end thereof leaves the sheet feed roller 9 and thereby rises upward.
In the collator 1 as constituted above, conventionally, when detection is conducted for the multiple feed of the prints 4 fed from each of the bins 2, a detection method has been employed in which the maximum value of the light transmission quantity of the prints 4 being passed is measured while the prints 4 pass through between the multiple feed sensors 15, and the maximum value is compared to a reference value.
However, in the conventional method as stated above, when the maximum value of the light transmission quantity of the prints 4 being passed is measured, a slack of the prints may develop as shown in FIG. 10B, and a springing of the prints may develop as shown in FIG. 10D. Therefore, the position of the sheet passing between the multiple feed sensors deviates from a predetermined position, thereby causing an increase in the light transmission quantity compared to the real one.
FIG. 11 illustrates an example of the light transmission quantity of the prints at the time of the sheet feed. This shows that when the slack or springing of the prints 4 develops as shown in FIGS. 10B and 10D, the light transmission quantity of the prints 4 drastically changes as shown in respective regions (i) and (ii) in FIG. 11 so that it cannot be stable.
Therefore, the conventional method as stated above may have caused a problem in that if the light transmission quantity of the prints 4, when the slack or springing of the prints 4 develops as shown in FIGS. 10B and 10D, is measured as the maximum value, the measured value is not less than a reference value even when a multiple feed really occurs, thereby causing misdetection.
Instead of the above method, it is known to use a method in which an average value of the light transmission quantity for a certain extent in area of the print is calculated and then the calculated average value is compared with a reference value.
However, in this method, when the level of the darkness of the printed portion is high or the rate of the printed portion to the whole area is high, as will be explained in the following examples 1 to 4 (FIGS. 12 to 15), a difference between the average values of the single feed and the multiple feed becomes smaller, thus causing a lower degree of accuracy for the detection.
As shown in FIG. 12, if the frequency at the light transmission quantity of 100 for the underlying portion of the prints is 50 and the frequency at the light transmission quantity of 40 for the printed portion of the prints is 50 at the time of the single feed, the average is 70. Assuming that the light transmission quantity for the underlying portion and the printed portion at the time of multiple feed may become a half compared with the single feed under such a condition, the average of the variations is 35. At this time, the variation in the light transmission quantity of the underlying portion is 50 and that of the printed portion is 20. This example 1 is for the case where the frequencies of the underlying portion and the printed portion of the prints are identical.
As shown in FIG. 13, if the frequency at the light transmission quantity of 100 for the underlying portion of the prints is 50 and the frequency at the light transmission quantity of 20 for the printed portion of the prints is 50 at the time of the single feed, the average is 60. Assuming that the light transmission quantity for the underlying portion and the printed portion at the time of the multiple feed may become a half compared with the single feed under such a condition, the average of the variations is 30. At this time, the variation in the light transmission quantity of the underlying portion is 50 and that of the printed portion is 10. This example 2 is for the case where the level of darkness of the printed portion of the prints is higher than that in the example 1.
As shown in FIG. 14, if the frequency at the light transmission quantity of 100 for the underlying portion of the prints is 80 and the frequency at the light transmission quantity of 40 for the printed portion of the prints is 20 at the time of the single feed, the average is 88. Assuming that the light transmission quantity for the underlying portion and the printed portion at the time of the multiple feed may become a half compared with the single feed under such a condition, the average of the variations is 44. At this time, the variation in the light transmission quantity of the underlying portion is 50 and that of the printed portion is 20. This example 3 is for the case where the frequencies of the underlying portion and the printed portion of the prints are different.
As shown in FIG. 15, if the frequency at the light transmission quantity of 100 for the underlying portion of the prints is 60 and the frequency at the light transmission quantity of 40 for the printed portion of the prints is 40 at the time of the single feed, the average is 76. Assuming that the light transmission quantity for the underlying portion and the printed portion at the time of the multiple feed may become a half compared with the single feed under such a condition, the average of the variations is 38. At this time, the variation in the light transmission quantity of the underlying portion is 50 and that of the printed portion is 20. This example 4 is for the case where the frequency of the printed portion of the prints is closer to that of the underlying portion than it is in the example 3.
Thus, the above mentioned examples 1 to 4 (referring to FIGS. 12 to 15) show that the smaller the quantity of the light transmission becomes as the level of the darkness of the printed portion of the prints becomes high, the smaller the average of the light transmission quantity becomes. These also show that the average of the light transmission quantity becomes small as the rate of the frequencies of the printed portion of the prints becomes large.
On the other hand, these also show that, focusing on only the variation in the underlying portion of the prints, the variations at the time of the single feed and the multiple feed are same.
FIG. 16 shows a frequency distribution representative of the light transmission quantity (analog-to-digital (A/D) converted value) when the prints pass between the multiple feed sensors. FIG. 16 shows that a histogram representative of the frequency at each of the A/D converted values indicates the clear discrimination between the xe2x80x9cunderlying portionxe2x80x9d enclosed with broken lines A and the xe2x80x9cprinted portionxe2x80x9d enclosed with broken lines B.
It is an object of the present invention to provide a method and device for detecting multiple feed capable of improving the accuracy of multiple feed detection over that currently in use and to overcome difficulties of the prior art, particularly by focusing on that the variation in the light transmission quantity of the xe2x80x9cunderlying portionxe2x80x9d of the prints is large at the time of the multiple feed.
To achieve the above object, according to an aspect of the present invention, there is provided a multiple feed detection device comprising: a sheet detector having a light emitting sensor and a light receiving sensor arranged in vicinity of a carriage path to detect quantity of light that has transmitted through a sheet; a memory which stores a predetermined sampling number of electric signals indicative of light quantity outputted from the sheet detector; and a processor which creates a histogram of the light quantity stored in the memory, obtains the light quantity corresponding to a maximum frequency for an underlying portion of sheets based on the created histogram, and detects a multiple feed of the sheets based on a variation in the light quantity of the maximum frequency.
In a preferred embodiment of the present invention, the processor scans frequencies from the light quantity indicative of a low level of darkness toward that indicative of a high level thereof and then detects a peak of the frequencies that satisfies a predetermined condition as the light quantity corresponding to the maximum frequency.
In a preferred embodiment of the present invention, the processor calculates a total sum of the frequencies corresponding to a predetermined number of the light quantities adjacent to a light quantity of interest, and detects one of the light quantities adjacent to the light quantity of interest as the light quantity corresponding to the maximum frequency if the total sum of the frequencies reaches a value which is a certain ratio of the predetermined sample value.
In a preferred embodiment of the present invention, the processor, at the time of feeding of a first sheet, regards a value that is a certain ratio of the light quantity corresponding to the maximum frequency as a reference value for detecting the multiple feed of the sheets, and at the time of feeding of a second or successive sheet, regards the light quantity corresponding to the maximum frequency as a comparison value and compares the comparison value with the reference value thereby to detect the multiple feed of the sheets.
To achieve the above object, according to another aspect of the present invention, there is provided a multiple feed detection method comprising the steps of: arranging a sheet detector having a light emitting sensor and a light receiving sensor in vicinity of a carriage path to detect quantity of light that has transmitted through a sheet; storing a predetermined sampling number of electric signals indicative of light quantity outputted from the sheet detector in a memory; creating a histogram of the light quantity stored in the memory; detecting the light quantity corresponding to a maximum frequency for an underlying portion of sheets based on the created histogram; and detecting a multiple feed of the sheets based on a variation in the light quantity of the maximum frequency.
In a preferred embodiment of the present invention, frequencies are scanned from the light quantity indicative of a low level of darkness toward that indicative of a high level thereof, and then a peak of the frequencies that satisfies a predetermined condition is detected as the light quantity corresponding to the maximum frequency.
In a preferred embodiment of the present invention, a total sum of the frequencies corresponding to a predetermined number of the light quantities adjacent to a light quantity of interest is calculated, and if the total sum of the frequencies reaches a value which is a certain ratio of the predetermined sample value, then one of the light quantities adjacent to the light quantity of interest is detected as the light quantity corresponding to the maximum frequency.
In a preferred embodiment of the present invention, at the time of feeding of a first sheet, a value that is a certain ratio of the light quantity corresponding to the maximum frequency is regarded as a reference value for detecting the multiple feed of the sheets, and at the time of feeding of a second or successive sheet, the light quantity corresponding to the maximum frequency is regarded as a comparison value and then the comparison value is compared with the reference value thereby to detect the multiple feed of the sheets.
The nature, principle and utility of the invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.